Brazing is a welding process that can employ heating by torch, furnace, induction, dip, resistance, twin carbon arc, flow and block-brazing processes. Brazing can be used for joining virtually all metals and dissimilar combinations of metals to one another, although not all combinations of dissimilar metals result in satisfactory joints. In brazing, coalescence is generally produced by heating above 800.degree. F. (427.degree. C.) but below the melting point of the metals being joined. A non-ferrous filler metal is typically used and has a melting point below that of the base metal. The filler metal is distributed in the closely fitted lap or butt joints by capillary attraction. Clean joints are generally essential for satisfactory brazing. The use of a flux or atmosphere to control surface cleanliness is usually required. Filler metal can be hand-held and fed into the joint (face feeding), or preplaced such as by rings, washers, shims, slugs or the like.
Brazing is considered to cover joints made by the flow of molten filler metal by capillary attraction, and encompasses the obsolete terminology of silver soldering, hard soldering and spelter brazing. Care should be taken to distinguish brazing from braze welding, which is a method of welding employing a filler metal which melts below the melting points of the base metals to be joined, but the filler metal is not distributed in the joint by capillary attraction.
Aluminum brazing requires close temperature control due to the melting points of the filler metals and the base metals falling into a narrow range. A flux is required to remove any aluminum oxide film and to prevent aluminum oxide from reforming. To avoid corrosion of the aluminum, the flux must be removed completely after brazing. Prebraze cleaning is essential for strong joints. The commonly brazed aluminum alloys are 1100, 3003, 3004, 5050, 6000 series and the A612, C612 casting alloys. The filler metals are Al--Si alloys and are supplied as wire, shims, paste mixtures of flux and alloy powder, or as brazing sheet. Torch brazing, furnace brazing and dip brazing are common processes used to achieve the finished joint.
In the past, various devices have been proposed for concentrically and radially aligning and welding together tubular metal components. For example see U.S. Pat. No. 4,084,739 disclosing an inflated elastic tubular member. In addition, it has been known to use a generally thin planar tool moved in radial direction with respect to the male tubing member to be joined for skiving, e.g. to slice off in a thin layer or to shave material from the tube prior to brazing, so that a small amount of material in the form of a mound or protuberance is built up, or plowed up, by the tool at generally opposing locations a predetermined distance from the end of the tube at an angle from one another less than 180.degree. and in the same general plane normal to the longitudinal axis of the tube prior to brazing. The plowed up material is supposed to center the tube end with respect to the receptacle during the brazing process. However, due to only two areas of material build up at less than 180.degree. from one another, typically the end of the tube is not properly centered with respect to the receptacle. One portion of the wall of the tube typically ends up in closer proximity to the wall of the receptacle leading to a joint of lower overall strength than desired. In addition, the tool narrows the wall thickness of the tube in the area where the tool is advanced to plow-up material, which may be unacceptable in certain applications.
Therefore, it is typical to encounter numerous problems with respect to brazing joints. Such problems can include non-uniform braze joints which can cause unacceptable leaks, weak braze joints, irregular braze gaps or the like. Leaking joints require additional rework which can be very costly, and weak braze joints can result in increased rates of field failure.